EP0238524B2 - Current transformer for a static electricity counter - Google Patents

Abstract

The current transformer arrangement on the secondary side with an integration stage is provided with a secondary winding consisting of two astatically designed coils (31, 32) lying next to one another and connected in series. As a result external parasitic magnetic fields have practically no effect on the transmission of the measured value. A large output signal from the secondary side is achieved by a large magnetic coupling of the primary conductor and secondary coil without the use of ferromagnetic materials. Preferably, the primary conductor (23) is designed as a flat conductor with suitably arranged slot-shaped recesses (25 to 28), so that primary windings (29a to 29g) are formed by changing the conductor cross-section (Fig. 5, 6, 7).

Description

The invention relates to a current transformer arrangement according to the preamble of claim 1.

Measuring large currents to determine energy consumption using static electricity meters requires the use of current transformers whose output signals must be suitable for further processing in electronic measuring units. The currents to be measured have magnitudes of more than 100 amperes, which must be detected up to the milliampere measuring range with slight linearity deviations. Such arrangements must be largely insensitive to direct current components in the measuring current. In addition, the consumption of auxiliary energy required to operate the arrangement should be as small as possible.

Furthermore, the requirements specified in IEC publication 521, in particular the galvanic isolation with high insulation strength, the short-circuit strength, the insensitivity to external magnetic interference fields and compliance with the frequency influence must be met.

The arrangement designed as a magnetic voltmeter according to DE-B-1 079 192 consists of two secondary coils connected in series, which comprise a busbar. The secondary partial windings are short-circuited at their ends with magnetic material. This results in a closed magnetic circuit (Rogowski coil), which is astatic to external fields, provided the winding density of the partial windings is sufficiently large and the winding distribution is even. In the case of large current densities in the primary conductor, the secondary coils must be at a certain distance from this in order to enable the partial voltages of the discontinuously distributed winding to be integrated perfectly.

The known current transformer arrangement is equipped with an electronic integrating stage, the frequency response of which is inversely proportional with respect to its input signal to the output signal, compensates for the proportional frequency dependence of the voltage induced in the secondary winding by the measuring current and which the input signal for the phase opposition of its output signal with respect to the current to be measured by a phase angle of 90 ° continues to shoot. The measuring signal at the output of the integrating stage is independent of the measuring frequency due to its effect and is in phase opposition to the measuring current with a direct proportionality between the amplitudes.

In the known current transformer arrangement, it is disadvantageous that the requirement for extensive insensitivity to external magnetic interference fields is not completely met by the use of magnetic material. Furthermore, the known arrangement delivers very small output signals since there is only a slight coupling between the fields of the primary conductor and the secondary coils. This method is therefore not suitable for measuring currents below about 1 kiloampere.

An active current sensor with a primary reducing winding is known from WO 83/01535, in which the error compensation is carried out with the aid of an indicator winding in such a way that a current is generated in the secondary winding by means of an amplifier which eliminates the induction in the magnetic core. A major disadvantage of this arrangement is the use of magnetic core material to generate sufficient magnetic coupling, since the magnetic material leads to considerable errors in DC components in the measuring current. A reduction in the primary-side flow is achieved by a primary winding wound in opposite directions from two conductors, in order to avoid saturation of the core by direct current flow.

A current transformer arrangement according to the preamble of claim 1 is described in JP-U-51 33 943. The axes of the secondary coils are perpendicular to the axis of the primary coils, so that inhomogeneous external fields cannot be compensated for.

The invention has for its object to improve a current transformer arrangement of this type in such a way that the influence of external magnetic interference fields is further reduced for a large measuring range of the order of milliamps to over 100 amperes and a high secondary-side output signal with a spatially small design and simultaneous use is cheaper Components is possible.

The achievement of the object according to the invention is characterized by the features of claim 1. In this arrangement, the secondary coil carrier has a permeability which is essentially independent of the magnetic field of the primary conductor. The secondary winding consists of two secondary coils connected in series, the secondary coil axes of which run parallel to one another. The direction of the turns of the secondary coils corresponds to that of a solenoid bent spatially by 180 ° in the middle. This astatic arrangement of the secondary coils leads to a secondary winding which is independent of external homogeneous magnetic interference fields, since the partial voltages induced by the interference fields in both secondary coils cancel each other out. While in the known secondary coils consisting of partial windings, the partial windings are always put together to form a closed integration path corresponding to a Rogowski secondary coil, the secondary coils in the invention extend in order to achieve small dimensions in each case only over a partial length of less than 50% of that generated by the current in the primary conductor Magnetic field lines, so that no closed integration path is formed. The second secondary coil primarily serves to compensate for the influence of external fields. With a view to the best possible compensation, the two secondary coils have small spatial dimensions and are arranged as close as possible to one another.

The secondary coils can be cylindrical or Flat coils with mutually parallel secondary coil axes run, at least one of the two secondary coils being spatially at a location at which the primary current generates the greatest possible field strength. The high field strength required for a high secondary-side output signal of the arrangement is achieved by shaping the primary conductor into a current loop. The secondary sub-coils thus only locally detect the magnetic field of the primary conductor, the sum of the voltages induced in the two secondary coils being proportional to the primary current to be detected.

A special feature of the new current transformer arrangement is its high magnetic coupling between the primary conductor and the secondary coil, so that large secondary-side output signals result, which enables the arrangement to be used for the linear detection of currents with currents down to a few milliamperes. This is achieved without using magnetic material. This results in a spatially small design, which enables inexpensive production.

The maximum magnetic coupling is achieved by the smallest possible distance between the primary current loop and at least one of the secondary coils. In order to record the magnetic flux of the primary current loop as completely as possible, the primary coil is practically arranged within the current loop.

In an expedient embodiment, two current loops with mutually opposite winding directions are arranged next to one another, one of the current loops being magnetically coupled to one of the secondary coils. The magnetic fluxes of these two current loops are opposite to each other.

In an advantageous embodiment, two current loops are connected in series, each current loop comprising a secondary coil. However, it is also possible for two current loops to be connected in parallel with one another and for each current loop to comprise a secondary coil. Here, the primary current to be measured is divided into two turns, so that folds can be avoided when the primary parts are preferably stamped out of copper with a rectangular cross section.

A very useful embodiment is characterized by the features of claim 5. Here, the primary conductor is folded around a transverse axis by an angle of 180 °, so that the forward and return conductors lie at a short distance above one another. This distance can be designed at least in sections so that the space created thereby is suitable for accommodating the secondary winding. In this embodiment, the magnetic interference influence on the measurement result is practically eliminated. Due to the shape and the small dimensions of the arrangement, fully automated production is made possible in a simple manner.

It is advantageous if the recesses extend in opposite directions, for example from the central axis to the edge of the flat conductor. As a result, the electrical current running in the longitudinal direction of the primary flat conductor is deflected to the center of the primary conductor, so that the current paths are formed into a loop.

In a further embodiment it is provided that the opposite conductor sections of the flat conductor each have two mutually opposite and parallel offset recesses and thereby form two sections of the current loop lying next to one another in the longitudinal direction of the flat conductor. In this case, the secondary coils are expediently located between the conductor sections of the flat conductor. Since the shape of the flat conductor leads to two adjacent sections of the current loop, the axes of which are each formed by the facing ends of the recesses, each secondary coil can be assigned to a primary winding, so that an optimal flux linkage is given.

A further advantageous embodiment results when the secondary coils in the construction of the planar technology are applied in one or more layers, possibly also on both sides as spirals on a substrate. This plate-shaped substrate can be inserted between the spaced conductor sections. The substrate with both secondary coils can also be arranged outside the space between the conductor sections over the effective winding surfaces of the primary flat conductor.

It is also possible for the substrate to contain further electronic components of the electricity meter. These can be, for example, the electronic components of the integration level and the multiplier level.

A further embodiment results from the fact that the one conductor section has two mutually opposite recesses which extend to the edge of the primary conductor on a common axis and to which a recess which does not extend to the edges is arranged in parallel on the other conductor section. With this arrangement of the recesses, the current paths are guided in such a way that two turns connected in parallel are formed, each of which are linked to the magnetic flux of a secondary coil.

The invention is explained below with reference to exemplary embodiments shown in the drawing. The known integration circuit has been omitted.

Fig. 1:

Eine Stirnansicht von zwei astatisch aufgebauten sekundären Spulen, von denen eine von einem Primärleiter umschlossen ist,

Fig. 2:

eine Stirnansicht von zwei astatisch aufgebauten Spulen, welche von in Reihe geschalteten Windungen des Primärleiters umschlossen sind,

Fig. 3:

eine Anordnung der sekundären Spulen nach Fig. 2, jedoch mit parallel geschalteten Windungen des Primärleiters,

Fig. 4:

die perspektivische Ansicht eines als Flachleiter geformten Primärleiters, bei welchem eine der astatisch aufgebauten sekundären Spulen zwischen gegenüberliegenden Leiterabschnitten des Flachleiters und die andere sekundäre Spule außerhalb des Flachleiters angeordnet sind,

Fig. 5:

eine perspektivische Ansicht eines Primärleiters in einer gegenüber Fig. 4 veränderten Ausführungsform,

Fig. 6:

die perspektivische Ansicht der astatisch aufgebauten Spulen der Sekundärwicklung mit einer Grundplatte, welche in den Primärleiter nach Fig. 5 einschiebbar ist,

Fig. 7:

eine Querschnittsdarstellung der Anordnung nach Fig. 5 und 6 im betriebsmäßigen Zustand in verkleinerter Darstellung,

Fig. 8:

die perspektivische Darstellung einer gegenüber Fig. 4 und 5 veränderten Ausführungsform des Primärleiters,

Fig. 9:

eine perspektivische Ansicht astatisch aufgebauter Flachspulen als Sekundärwicklung auf einer Grundplatte, welche in den Primärleiter nach Fig. 8 einschiebbar ist,

Fig. 10:

eine perspektivische Darstellung eines zur Fig. 8 vergleichbaren Primärleiters mit darin angeordneten Spulen der Sekundärwicklung,

Fig. 11:

die Draufsicht auf einem aufgeklappten als Flachleiter ausgebildeten Primärleiter,

Fig. 12:

eine Draufsicht auf den Primärleiter nach Fig. 11 im gefalteten Zustand,

Fig. 13:

eine Draufsicht auf eine Grundplatte mit astatisch aufgebauten Flachspulen in einer mit Fig. 9 vergleichbaren Bauweise,

Fig. 14:

eine Draufsicht auf den gefalteten Primärleiter nach Fig. 11 auf die gegenüber Fig. 12 entgegengesetzte Seite und

Fig. 15:

einen Querschnitt der Anordnung nach Fig. 14.

Show it:

Fig. 1:

A front view of two astatically constructed secondary coils, one of which is enclosed by a primary conductor,

Fig. 2:

3 shows an end view of two astatically constructed coils, which are enclosed by turns of the primary conductor connected in series,

Fig. 3:

an arrangement of the secondary coils 2, but with parallel turns of the primary conductor,

Fig. 4:

the perspective view of a primary conductor shaped as a flat conductor, in which one of the astatic secondary coils is arranged between opposite conductor sections of the flat conductor and the other secondary coil is arranged outside the flat conductor,

Fig. 5:

3 shows a perspective view of a primary conductor in an embodiment modified from FIG. 4,

Fig. 6:

the perspective view of the astatically constructed coils of the secondary winding with a base plate which can be inserted into the primary conductor according to FIG. 5,

Fig. 7:

5 and 6 in the operational state in a reduced view,

Fig. 8:

4 shows a perspective illustration of an embodiment of the primary conductor that has been modified compared to FIGS. 4 and 5,

Fig. 9:

8 shows a perspective view of astatically constructed flat coils as a secondary winding on a base plate which can be inserted into the primary conductor according to FIG. 8,

Fig. 10:

8 shows a perspective illustration of a primary conductor comparable to FIG. 8 with coils of the secondary winding arranged therein,

Fig. 11:

the top view of an unfolded primary conductor designed as a flat conductor,

Fig. 12:

11 shows a plan view of the primary conductor according to FIG. 11 in the folded state,

Fig. 13:

3 shows a plan view of a base plate with astatically constructed flat coils in a construction comparable to FIG. 9,

Fig. 14:

a plan view of the folded primary conductor of FIG. 11 on the opposite side to FIG. 12 and

Fig. 15:

a cross section of the arrangement of FIG. 14th

1 shows two astatic cylindrical coils 1 and 2 of a secondary winding 3 arranged at a distance. The coils 1 and 2 held by a spacer 4 are geometrically and electrically identical and run parallel to one another with their cylinder axes. The coils 1 and 2 are arranged in an insulating cylinder 5 and 6. The coil 1 is surrounded by a turn 7a of the primary conductor 7 through which the measuring current I 1 flows in the direction of the arrows indicated. The voltages induced in the coils 1 and 2 by the magnetic field of the alternating current flowing in the primary conductor 7 add up to a signal proportional to the alternating current I 1 to be measured. Voltages induced by homogeneous external interference fields have different signs due to the astatic arrangement of coils 1 and 2 and cancel each other out. This measure largely suppresses the influence of external alternating magnetic fields on the correct functioning of the current transformer arrangement. The influence of external fields can be further reduced by the magnetic shielding material surrounding the coils.

In Fig. 2, the coils 8 and 9 correspond to the coils shown in Fig. 1. The secondary coils 8 and 9 are successively embraced by the common primary conductor 10. This series connection of the primary windings 10a and 10b leads to an enlarged measurement signal compared to the arrangement according to FIG. 1.

In FIG. 3, the coils 11 and 12 correspond to the coils 8 and 9 in FIG. 2. The primary conductor 13 is branched onto two partial conductors which are each formed into a winding 13a or 13b which surrounds the coil 11 or 12. The current I 1 is branched onto the partial conductors with the windings 13 a and 13 b, the sum of the voltages induced in the coils 11 and 12 being proportional to the current I 1 to be measured. The advantage of the arrangement according to FIG. 3 compared to the embodiment according to FIG. 2 is that, in the case of the primary conductor 13 with a rectangular cross section (flat conductor) stamped out of copper, folds can be avoided when the conductor parts are crossed.

In the embodiment according to FIG. 4, a primary conductor 14 is designed as a flat conductor with a rectangular cross section, which is folded in such a way that opposite conductor sections 14a and 14b result in a cuboidal cavity 15. Outside the cavity 15, opposite sections of the primary conductor 14 are separated from one another by an insulating layer 16. The conductor section 14a is equipped with a slot-shaped recess 17 extending from approximately the center to the edge. A recess 18 extending in the opposite direction to the edge is provided on the opposite conductor section 14b. The recesses 17 and 18 influence the geometric position of the current paths of the current to be measured represented by the arrows 19 and 20 such that a turn is formed for the primary current. The secondary coil 21, shown in broken lines, is arranged in the magnetic field of this turn. A second secondary coil 22 is located outside the primary conductor to compensate for external magnetic fields.

The primary conductor 23 shown in FIG. 5 differs from the embodiment according to FIG. 4 in that two opposite slot-shaped recesses 24 and 25 or 26 and 27 are provided in the opposite line sections 23a and 23b. The laterally open recesses 24 to 27 each extend approximately to the middle of the conductor sections 23a and 23b. The recesses 24 and 26 are in the same plane perpendicular to the primary conductor 23 when it is folded by 180 ° in the operational state, that is to say the conductor sections 23a and 23b run parallel to one another. In the same way, the recesses 25 and 27 are arranged in a common plane perpendicular to the primary conductor 23.

Due to the above design of the recesses 24 to 27, the primary current runs on current paths which are identified by the arrows 29a to 29g. As a result, primary windings connected in series are formed in the planes of the conductor sections 23a and 23b, in whose magnetic field secondary coils can be arranged.

On the base plate 30 shown in FIG. 6 there are two astatically arranged secondary coils 31 and 32. In the operational state, the base plate 30 with the coils 31 and 32 is located between the conductor sections 23a and 23b of the primary conductor according to FIG Coil 31 in FIG. 6 is identified on line section 23b in FIG. 5 by the dashed circle 33. Correspondingly, the coil 32 in FIG. 6 is located in an area represented by the circle 60 shown in broken lines in FIG. 5.

FIG. 7 shows the current transformer arrangement with the part on the primary side according to FIG. 5 and the part on the secondary side according to FIG. 6 in the operational state. Here, the upper and lower sections of the primary conductor 23 are separated from one another by an insulating layer 61.

The primary conductor 34 in FIG. 8 is comparable to the primary conductor 23 in FIG. 5. Only the distance between the upper conductor section 34a and the lower conductor section 34b is smaller and corresponds to the thickness of the insulating layer 35.

The base plate 36 shown in FIG. 9 with the secondary coils 38 and 39 arranged thereon is in the operational state of the current transformer arrangement between the conductor sections 34a and 34b of the primary conductor 34 according to FIG. 8. The coils 38 and 39 in FIG. 9 are constructed in a spiral shape and made in planar technology so that the small space between the conductor sections 34a and 34b of FIG. 8 is sufficient. In the operating state, the center of the coil 38 is approximately at the central end of the slot-shaped recess 40 in FIG. 8. Accordingly, the center of the coil 39 and the central end of the recess 41 are arranged approximately congruently.

FIG. 10 shows a primary conductor 42 which essentially corresponds to the primary conductor 34 in FIG. 8. However, the recesses 44 and 45 are formed as holes at their end facing the center of the primary conductor 42, in which astatic secondary coils 46 and 47 are mounted.

In the embodiment according to FIG. 11, a primary conductor 48 is shown open, that is to say before folding around a line 49. In the folded state, a conductor section 48a is located above a conductor section 48b. The conductor section 48b shows recesses 50 and 51 which face each other and run parallel to the folding line 49 on a common longitudinal axis. A recess 52 is provided on the conductor section 48a, which runs only in the central region of the conductor section 48 and is at the same distance from the folding line 49 as the recesses 50 and 51. The locations for the secondary coils are shown by the dashed circles 53 and 54. For this purpose, the corresponding base areas 55 and 56 are located for the secondary coils in mirror symmetry with respect to the folding line 49.

FIG. 12 shows the primary conductor 48 according to FIG. 11 in a folded form, so that the conductor sections 48a and 48b lie one above the other. Correspondingly, only the recesses 50 and 51 with the locations for the secondary coils, which are indicated by circles 53 and 54.

13 shows the secondary coils 56 and 57 fastened on a base plate 55 in an astatic design. This arrangement, which corresponds in principle to FIG. 9, differs from this essentially in that the coils 56 and 57 in FIG. 13 are at the same distance from the folding line 49. The coils 56 and 57 can also be manufactured using planar technology. In order to expose both coils to the corresponding primary magnetic flux, they can also be arranged outside the space between the folded conductor sections 48a and 48b according to FIG. 11, provided that the magnetic coupling is sufficient for a high output signal. In this case too, the circles shown in FIGS. 11 and 12 are the corresponding locations for the secondary coils.

FIG. 14 shows the primary conductor 48 according to FIG. 11 in the folded state from the opposite side in comparison to FIG. 12. Accordingly, only the central recess 52 can be seen.

The primary conductor 48 can also be seen in the folded state in FIG. 15, the distance between the upper conductor section 48a and the lower conductor section 48b being determined by an insulating layer 57. The direction of the primary current to be metered is indicated by arrows 58 and 59. The base plate 55 according to FIG. 13 is inserted into the space 70.

Claims (10)

1. A current transformer arrangement, in particular for a static electricity meter, comprising a primary conductor (7, 10, 13, 14, 23, 34, 42, 48) carrying the alternating current to be measured, and a secondary winding which comprises at least two series-connected electrically identical coils of an astatic configuration and which is coupled to the primary conductor without magnetic materials, characterised in that to produce a maximum magnetic field strength the primary conductor (7, 10, 13, 14, 23, 34, 42, 48) is formed into at least one current loop (7a, 10, 10b, 13a, 13b, 29c, 29e), that at least one of the secondary coils (1, 8, 11, 12, 21, 22, 31, 32, 38, 39, 46, 47, 56, 57), for maximum magnetic coupling, is arranged at the smallest possible spacing relative to the corresponding current loop (7a, 10, 10b, 13a, 13b, 29c, 29e) and practically within same, that the secondary coils (1, 8, 11, 12, 21, 22, 31, 32, 38, 39, 46, 47, 56, 57) extend in their axial direction over a smallest possible part of the length of the magnetic field lines produced by the current in the primary conductor, that the secondary coils (1, 8, 11, 12, 21, 22, 31, 32, 38, 39, 46, 47, 56, 57) are arranged in as closely adjacent juxtaposed relationship as possible for optimum external field compensation, and that to produce a measurement signal which is independent of frequency an electronic integration stage on the output side is applied to the output of the secondary coils (8, 9, 11, 12).
2. A current transformer arrangement according to claim 1 characterised in that two current loops (10a, 10b, 13a, 13b) with mutually oppositely directed winding directions are arranged side-by-side and a respective one of the current loops is magnetically coupled to one of the secondary coils (8, 9, 11, 12).
3. A current transformer arrangement according to claim 1 or claim 2 characterised in that two current loops (10a, 10b) are connected in series and each current loop (10a, 10b) embraces a secondary coil (8, 9).
4. A current transformer arrangement according to claim 1 or claim 2 characterised in that two current loops (13a, 13b) are connected in parallel with each other and each current loop (13a, 13b) embraces a secondary coil (11, 12).
5. A current transformer arrangement according to one of the preceding claims characterised in that the primary conductor (14, 23, 34, 42, 48) is in the form of a folded flat conductor with mutually oppositely disposed conductor portions (14a, 14b, 23a, 23b, 34a, 34b, 48a, 48b) which, by means of at least one opening (17, 18, 25 to 28, 50 to 52), each form at least one portion of the current loop (29c, 29e) in the plane of the flat conductor.
6. A current transformer arrangement according to claim 5 characterised in that the openings (17, 18, 22 to 28) extend in mutually opposite directions approximately from the centre line to the edge of the flat conductor.
7. A current transformer arrangement according to claim 6 characterised in that the oppositely disposed conductor portions of the flat conductor each have two mutually oppositely directed openings (25 to 28) which are arranged in parallel displaced relationship and thereby form two portions of the current loop (29c, 29e) which are disposed side-by-side in the longitudinal direction of the flat conductor (23).
8. A current transformer arrangement according to one of claims 5 to 7 characterised in that the secondary coils are arranged between the conductor portions of the flat conductor.
9. A current transformer arrangement according to claim 7 or claim 8 characterised in that the secondary coils (38, 39), being produced by the planar technique, are disposed in one or more layers in the form of spirals on a substrate.
10. A current transformer arrangement according to claim 5, claim 8 or claim 9 characterised in that the one conductor portion (48b) has two mutually oppositely directed openings (50, 51) which extend to the edge of the flat conductor (48) on a common axis and arranged in parallel therewith on the other conductor portion (48a) is an opening (52) which does not go to the edges.

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